Graphene is in the form of a two-dimensional crystal of carbon atoms and great attention has been focused on graphene as industrial material since its discovery in 2004. Graphene has excellent electric, thermal, optical, and mechanical characteristics, and there are growing expectations for its applications in wide areas such as production of battery materials, energy storage materials, electronic devices, and composite materials.
To realize such applications of graphene, it is essential to develop efficient production methods for cost reduction and improve the dispersibility.
Methods available for the production of graphene include the mechanical exfoliation method, CVD (chemical vapor deposition) method, and CEG (crystal epitaxial growth) method, but these methods are so low in productivity that they are not suitable for mass production. Compared to this, the oxidization-reduction method (oxidized graphite, also called oxidized black lead, is produced first through oxidization of natural graphite, followed by converting it into graphene through reduction reaction) is a very important means of practical manufacturing of graphene because it can serve for large-scale synthesis of graphene.
Graphene not only has high electric conductivity, but also has a thin, flat structure to serve for forming a large number of conductive paths, and accordingly, it has a high potential particularly as a conductive material for batteries. However, graphene is a kind of nanocarbon and tends to undergo agglomeration easily. If produced by simply carrying out oxidization and reduction, therefore, the resulting graphene will not be able to disperse moderately in the matrix to realize its full potential.
In Patent document 1, graphene oxide is expanded and exfoliated while it is heated for reduction in order to produce thin layers of graphite with a large specific surface area.
In Patent document 2, graphene is chemically reduced in the presence of catechol and subsequently freeze-dried to prepare a graphene powder with high dispersibility.
In Patent document 3, graphene oxide is chemically reduced in the presence of a water-soluble compound having a 9,9-bis-(substituted aryl)-fluorene backbone and the resulting aqueous graphene sedimentation is mixed with an organic solvent. Then, graphene is recovered by centrifugal sedimentation and an organic solvent is added to prepare a graphene/organic solvent dispersion.